This invention pertains to hydraulic fluids and in particular to those having excellent water tolerance at -40.degree.C.
Power transmission or hydraulic fluids, and particularly brake fluids are subject to moisture contamination which may arise because of the inherent hygroscopicity of the hydraulic fluid, from condensation of moisture from the air or from physical leakage or defects in the hydraulic system which permits the entry of water. The deleterious effects arising from moisture contamination of hydraulic fluids include lowering of boiling points, vapor locking, corrosion, hydrolysis, foaming, sludging, freezing and the like. Such contamination is especially serious in on- and off-highway automotive central hydraulic system fluids which function in any one or a combination of power units engineered to operate windows, seats, steering mechanisms, brakes, aerials, starters and the like. Federal Motor Vehicle Safety Standard No. 116 as published in the Federal Motor Vehicle Safety Standards and Regulations, Supplement 80, dated Oct. 23, 1974 lays down specific requirements for hydraulic brake fluids including test procedures such as S5.1.9 for water tolerance. This regulation requires that in accordance with test S6.9.1 and S6.9.3 a DOT 5 brake fluid when humidified and stored at -40.degree.C. for 120 hours shall show no sludging, sedimentation, crystallization, or stratification.
The use of non-petroleum types of materials as hydraulic fluids was initiated because of the need for compatibility with the natural rubber and synthetic rubber seals used in hydraulic systems, such as for example those used in automotive brake systems. Among the newer types of hydraulic fluids examined in recent years are the silicone brake fluids which meet many of the swell, boiling point, corrosion and other properties but do not meet the water tolerance test for DOT 5 silicone brake fluids enumerated above.
It is therefore an object of this invention to provide silicone hydraulic fluids which meet the water tolerance requirements of DOT 5 silicone type brake fluids.
Other objects will become apparent to those skilled in the art upon a reading of the specification.